The present invention relates in general to the treatment of production fluid from petroleum wells at the site of the well, and, in particular, to the breaking of an oil-water emulsion of production fluid from petroleum wells.
An oil and water emulsion in production fluids from petroleum wells is preferably broken at the well site. One method of emulsion breaking practiced in the past combined emulsion breaking chemicals, settling, heat, and an alternating electrostatic field. In this technique, production fluid containing the emulsions feeds into a separation vessel. Gas in the production fluid flows out a gas line after losing entrained condensate against baffles. The liquid, including the emulsion, initially dwells in an annular space around a fire box. Time and some heat from the fire box win some emulsion breakdown in the annular space. Free water accumulates at the bottom of the annular space and flows out through a free water conductor into a water chamber of the vessel. Emulsions above the water flow into a space on the outside of the fire box for heating the emulsions. Heated emulsion flows into a chamber beneath an emulsion spreader that spreads the emulsion out over the entire horizontal extent of an electrical coalescing section of the vessel. Rising emulsions are subjected to an alternating electrostatic field in the coalescing section and experience emulsion breaking by polarization of water molecules and a resultant coalescence of the molecules. The coalesced water drops to the bottom of the vessel into the water chamber. Water leaves the vessel through a water outlet. Oil leaves the vessel through an oil valve.
This technique of emulsion breaking requires the use of a heater. It is not desirable in many environments.
The concept of centrifugal separation of the phases of production fluid from a petroleum well is known. U.S. Pat. No. 3,982,589 to Phillip Wilson, John Erickson, Charles Nelson, and Vitolis Budrys discloses an apparatus and method for producing power fluid for production purposes. The patent states that power fluid produced from well production fluid may be used in the well to power machinery in the well. The power fluid may be pressurized at the surface by a high pressure pump and fed downhole for operating downhole machinery, for example. The fluid must be free of solid contaminates to avoid damage to the fluid handling machinery. Typically, the fluid is separated at the surface by gravity separation into water, oil, and gas phases. Usually water from the separation is used as the power fluid, although oil may be used. The Wilson et al patent discloses a phase separation vessel at the site of a petroleum well. Production fluid from the well goes into this vessel and separates into its phases by gravity. This produces the fluid that will be used as the power fluid. This fluid is withdrawn through a line and treated by a centrifugal, pitot type separator. The separator separates the fluid into a stream of dirty liquid containing undesirable solids, a stream of any entrained gas, and a stream of desired power fluid. The power fluid is then fed into the high pressure pump and from there into a well.
Many types of pitot separators are known. One is described in U.S. Pat. No. 3,817,446 to J. W. Erickson et al. Another is described in U.S. Pat. No. 4,036,427 to J. W. Erickson et al.
Schemes using cyclone separators also are being used to condition production fluid. Difficulties with the cyclone separation include the sensitivity of the separators to fluid flow rate and operating pressure. Examples of the use of such separators are described in U.S. Pat. No. 3,709,292 to Palmour and U.S. Pat. No. 3,802,501 to Mecusker.